1) Field of the Invention
The invention relates to an optical sensing system, in particular, a retinal focal-plane sensor chip that is structured on Pseudo Bipolar Junction Transistor (Pseudo-BJT) and comprises a system with an adaptive current Schmitt trigger and a smoothing network for optical image detecting circuits, such as image identification, image tracing, robot vision readers of image, barcode or character, etc.
2) Description of the Prior Art
Rapid development of science and technology has made the semi-conductor and IT industries continuously rising and flourishing, resulting in outstanding changes in considerable application fields. Such changes not only make achievement of science and technology, but also improve our quality of life and alter our patterns of life. Since 1980, the researches in silicon retina have been developed one after another emphasizing how to attain the H cell function by circuits applying Gaussian smoothing to signals. How to enable retina and cerebrum visual functions to be performed by silicon chip has become a great challenge in recent years. In the event that silicon retina and silicon neural network can be developed, human visual system functions or its partial functions can be attained in electronic systems to greatly enhance the capability of instant image processing system and further be applied to the fields of image recognition, image tracing and robot vision.
An organism's retina is an excellent instant image sensing and front-end processing system with the advantages of high dynamic range and instant image processing, hence, more and more R&D people are attracted to research the possibility of using IC for realizing the retina function.
Among those researches, the most attractive structure was Resistor Network proposed by Caver Mead. The structure employed photo bipolar junction transistor (PBJT) to convert light into electric signal and simulate the sensitization of P cell. Subsequently, the signal is implanted into the Resistor Network generating similar Gaussian smoothing signal for simulating the H cell function. Consequently, both signals subtract each other obtaining a B cell signal. The Resistor Network in this structure is only composed of megaohms resistance; however, a large resistance still occupies a larger chip area during the Integrated Circuit(IC) design. Even though there have been various researches and methods for improving the drawback mentioned above, nevertheless, the chip area of silicon retina of Resistor Network is still too large. In addition to the above drawbacks of Resistor Network, there are two problems while PBJTs are applied: (1) the chip area is large when BJT-based retinal sensor is manufactured; (2) the PBJTs have smaller current gain when the technology scales down to 0.25 um or below. In view of the drawbacks and problems mentioned above, it is obvious that BJT-based technique is not suitable to be applied in the future manufacturing and optical applications.